Thermoplastic resins are used for a variety of purposes due to excellent moldability thereof. Of the thermoplastic resins, use of engineering plastics in auto parts, structural parts, electric and electronic parts has been expanding making use of heat resistance thereof. In the field of electric and electronic parts, while efforts are being made to reduce weight, thickness and size and improve performance, safety at the time of use, productivity, use of reclaimed resources and the like are desired. Therefore, the application of thermoplastic resins, mainly polyester resins which have excellent heat resistance, moldability and chemical resistance and are easy to be flame-retarded, has been growing more than thermosetting resins.
When these thermoplastic resins are used in electric and electronic parts, they are generally reinforced with fibrous reinforcements and flame-retarded with halogen-based flame retardants typified by bromine-based flame retardants in order to improve the strength and safety of products comprising such parts.
Although thermoplastic resins themselves have high tracking resistance, one of the measures of electric insulating properties, the tracking resistance of the thermoplastic resins greatly lowers when they are reinforced and flame-retarded, whereby the risk of a fire rises despite the acquired flame-retardancy.
Many attempts have been made to improve the tracking resistance of the thermoplastic resins. For instance, blending of a metal oxide, metal silicate compound or the like with the thermoplastic resins has been proposed. This, however, has resulted in a reduction in mechanical properties in many cases.
Under such circumstances, a thermoplastic resin having excellent mechanical properties, flame retardancy and tracking resistance has been strongly desired.
Mitsubishi Electric Technical Report Vol. 69, No. 4 (1995) reports at pages 40 to 43 that when an overcurrent tripping test was made on reinforced resin compositions prepared by compounding aluminum borate whiskers, aluminum silicate fibers, E glass fibers, wollastonite, illite, mica or potassium titanate whiskers with nylon 46, aluminum borate whiskers, aluminum silicate fibers and wollastonite cut off a current more frequently than glass fibers, which are generally used as an inorganic reinforcement for resins, whereas potassium titanate whiskers and mica cut off a current less frequently than the glass fibers. The above report discloses no resin compositions comprising both a flame retardant and a reinforcement.
JP-B 6-4765 discloses a resin composition prepared by compounding aluminum borate whiskers with a resin (excluding a polyvinyl chloride resin). This publication discloses a flame retardant as one of additives that may be added to the resin composition as required. However, it shows no specific examples of the flame retardant or problems accompanied with the use of a flame retardant.